Parenchymal cells may accumulate normal (water, proteins, etc) or abnormal (mutated proteins, infectious agents, etc) substances in their nuclei or cytoplams (typically in phagolysosomes). These substances can be produced by the cell (endogenous) or elsewhere but stored in the cell (exogenous). This can be harmless for the cell or toxic. Here are some examples of accumulations. Fatty Change or Steatosis Cholesterol & Cholesteryl esters Proteins Glycogen Pigments These can accumulate in the cell via 4 main pathways: Abnormal metabolism (can't remove endogenous substance) - e.g. fatty change in liver and heart Abnormal folding, transport, or degradation of endogenous proteins - e.g. α1-antitrypsin in liver cells Storage diseases: Defect in enzymes that metabolize lipids and carbs -> accumulation of endogenous lipids and carbohydrates in usually lysozymes Ingestion of indigestible materials - cell takes in exogenous substances that it can't metabolize or transport elsewher